Curable silicone compositions are widely used by way of example as sealants and coating materials. Two-component systems composed of a vinyl-functional polysiloxane and of a SiH-functional polysiloxane as a crosslinking agent are very widely used.
The crosslinking reaction takes place through noble-metal-catalyzed hydrosilylation, mostly using platinum complexes. By way of example, U.S. Patent Application Publication No. 2004/0116640 A1 describes a two-component silicone resin composition for producing light-emitting diodes (LEDs) which is hardened thermally after addition of platinum catalysts. Another form of the crosslinking method is light-induced hydrosilylation—also termed photohydrosilylation—and this has been described in many publications including, for example, DE 069019058 T2, DE 069122625 T2, U.S. Pat. No. 6,127,446, WO 2006055456 A1, JP 2010047646 A1 or WO 2009092762 A1. U.S. Patent Application Publication No. 2007/0141739 A1 describes the combination of light-induced and thermally activated hydrosilylation reactions. WO 2010049388 A1 describes a sequential combination of the crosslinking reactions, in that the first step of exposure to light causes insipient crosslinking of the cast silicone part to achieve dimensional stability and a second step cures the entire material thermally.
There are many publications disclosing selected silicone resin formulations constituted from two or more components, where the mechanical, thermal and optical properties of the hardened silicone are adjusted through the proportion of a highly crosslinked resin in the liquid composition, as described by way of example in WO 2010087523 A1, or else by dispersing solid fillers, such as silica, described in JP 2010018662 A1, into the material.
In order to improve adhesion of the sealants and embedding compositions on the substrates and contact areas, it is possible, as described by way of example in U.S. Patent Application Publication No. 2010/0256300 A1 to use alkoxysilanes as adhesion promoters.
A difficulty with the use of multicomponent systems is the stability of the preparation. Partial demixing of incompatible silicones or silanes or precipitation of the solid fillers can cause phase separation and defects in the cured components. The viscosity of formulations of this degree of complexity can also place limits on ease of use if, for example, undesired air inclusions do not escape rapidly. If domains with different crosslinking level are formed during hardening, the resultant variation of mechanical properties leads to an inhomogeneous material with preferential breakage points.
Curable single-component silicone compositions are preferably used in order to avoid the disadvantages described for the multicomponent systems. By way of example, WO 2006/055456 A1 mentions inter alia the use of a single-component silicone resin for producing LEDs through photohydrosilylation.
WO 2008/036662 A1, WO 2008/036657 A1 and EP 0490401 A1 describe linear vinylhydropolysiloxanes and uses of these. DE 102009015211 A1 describes enzyme preparations which are produced with the aid of vinylhydropolysiloxanes, where these can be linear or branched, and can comprise polyether substituents.
U.S. Pat. No. 4,339,564 A1 describes vinylhydropolysiloxanes branched by way of C6H5—SiO3/2 units. In that document, and in U.S. Pat. No. 4,578,493 A1 single-component silicone compositions are also described, where the SiH functions are pendant in the siloxane chain. U.S. Patent Application Publication No. 2007/265410 A1 describes a process for producing single-component silicone compositions of this type through hydrolysis and condensation of chlorosilanes. Contact with aqueous hydrochloric acid liberated during the process degrades some of the pendant SiH groups in the siloxane chain to give SiOH groups, and makes it more difficult to control the level of precrosslinking in the liquid silicone composition.
WO 2010/129123 A1 describes curable single-component silicone compositions having pendant and/or terminal SiH functions and pendant vinyl functions, where these can comprise SiOH groups. The siloxanes are produced through reaction of chlorosilanes in the presence of water. The siloxanes can comprise SiOH groups, and condensation of these produces water, which evaporates slowly and has to be removed by heating in order to achieve complete hardening. The curable single-component silicone compositions described in WO 2010/129123 A1 comprise the majority of the reactive vinyl and SiH functions pendant in the silicone chain.
WO 2003/080753 A1 describes curable single-component silicone compositions which have branching by way of R—SiO3/2 units and by way of SiO4/2 units and which comprise no R2SiO2/2 units. Very hard materials are obtained, with very low coefficients of thermal expansion. When materials with this level of brittleness are exposed even to low levels of mechanical stress, lack of elasticity can cause hair cracking which reduces the weathering resistance of the material.
In view of the above, there is a need to provide a curable single-component silicone composition which hardens rapidly and homogeneously, preferably adheres well to the substrate and contact areas, and at the same time preferably requires no additional deaerator.